I don't mind being up high, I actually enjoy it quite a bit! I just don't love looking down over the edge (well, it looks like you're looking down over a ledge?) I've actally stood on a glass floor over the Grand Canyon here in America. It's a little weird to look down at your feet and see a gigantic fall between your feet and the canyon floor.
I love being up high and would have no problem looking down through a glass floor (though it does sound brilliant) I don't like the feeling of falling though. I don't think I could parachute or bungee.
Here's a semi-good picture of the place I'm talking about [link] I didn't have any problems when I was on it, though the thought of walking on glass with a bunch of other people at the same time is kind of frightening. I'm the person that will look over the edge of a balcony when I'm on the 50th floor of a building though.. Even though I'm not a fan of heights. I'm not sure I understand my own logic. Bungee jumping sounds like the most terrifying thing anyone could do. I don't like the idea of being pulled backward and falling again. Being jerked around isn't enjoyable. But if I was 500% sure that there would be no chance of an accident happening, I'd go parachuting in an instant!